In some cases fault finding or criticizing does not fall under backbiting: 1) If the oppressed person complains of the oppressor seeking redress, it is not backbiting. Allah says about it: Allah does not love open utterance of evil in speech except by one who has been wronged” (Qur’an, 4:148). 2) To relate anyone’s fault while giving advice is not backbiting because dishonesty and duplicity is not permissible in counseling.
3) If, in connection with seeking the requirements of a religious commandment, the naming of a particular individual cannot be avoided, to state the fault of such a person to the necessary extent will not be backbiting. 4) To relate the misappropriation or dishonesty committed by someone with a view to saving a Muslim brother from harm will not be backbiting. 5) To relate the fault of someone before one who can prevent him from committing it is not backbiting. 6) Criticism and expression of opinion about a relater of traditions is not backbiting. 7) If a person is well acquainted with someone’s shortcoming, then to relate such a fault in order to define his personality, for example, describing a deaf, dumb, lame or handless person as thus, is not backbiting. 8) To describe any fault of a patient before a physician for purposes of treatment is not backbiting. 9) If someone claims wrong lineage, to expose his correct lineage is not backbiting. 10) If the life, property or honor of someone can be protected only by informing him of some fault, it will not be backbiting. 11) If two persons discuss the fault of another, which is already known to both, it will not be backbiting, although to avoid discussing it is better, since it is possible one of the two might have forgotten it. 12) To expose the evils of one who openly commits evils is not backbiting as the tradition runs: “There is no backbiting in the case one who has torn away the veil of shamefulness.”
Nahjul Balagha translated by Yasin T. Jibouri Commentary to Sermon 138